subfloor question need help

Old 01-13-07, 08:08 AM
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subfloor question need help

Hiya I'm a fairly new homeowner and within a month or two of owning my house a freak accident caused a pipe on my first floor to break under my sink. The resulting flood got into my finished basement and ruined all the carpeting down there. I tore it up and found just an uneven concrete floor, I want to put down some new self adhesive linoleum tiles I bought but thought laying a subfloor would be wise. I cut some ply and after doing a dry lay tried using Liquid Nails subflooring adhesive to attach it to the concrete. So far its not been strong enough on its own, my questions are the following.

1. I've read on here about stronger construction grade adhesives such as PL Urathanes would that be a better choice for attaching the ply?

2. Also many folks on here seem to be using screws as well, but as far as I can tell thats usually into wooden joists and whatnot. Can I use screws to help the adhesive work better into concrete? If so, what screws could you recommend and will I need to drill with a Hilti or something first to lay in anchors?

thanks in advance for any help ^^
Old 01-13-07, 11:03 AM
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I've never done it myself, but have seen others on this forum who have advised to use Tapcon screws. I did a little search for them and they're easy to find, look like they'd do the job, and there are instructions with pictures. They also look pretty time consuming. I use PL400 to glue tack strip to concrete and, provided the concrete is dry and clean, it holds under the stress of stretching carpet. I'm not sure how long it would take to set up enough to do it's job under the conditions you're in. With tack strip, it has air to it and the part under the strip doesn't have far to travel to wick out whatever has to dissipate in order to cause it to hold. The stuff in the center of the panels may not dry as quickly so you might have to weight it down longer. All this is pure speculation on my part, however.
Old 01-13-07, 01:52 PM
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Well I was using weights with just the liquid nails anyhow so I would probably use the same on any PL, as for the screws I'll check'em out. Anyone else with advice please feel free to chime in, thanks in advance.
Old 01-13-07, 03:19 PM
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The Hilti sounds like the best idea.
It will be hard to control the wood warpage with this application.
Old 01-13-07, 05:15 PM
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First off, you mention you have an uneven floor.
Thats the 1st item to address.
Once dry, use a self leveling flooring compound, usually easily obtainable from the 'big box' stores...and level your floor.
Once that is done, what I/we have done in the restoration company I work with, is lay 8mil poly down on the concret floor, tape overlapping seams, then lay the 2x4 on side, framing out the floor. Drill a hold threw the 2x4's and into the concret (masonary bit) the size of a 3" common nail, stick a piece of bailing wire the length of the nail into the hole and nail the 2x4 down.
Holds pretty damn good. Then lay your subfloor, usually t&g 5/8" ply
Old 01-15-07, 11:37 PM
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you are trying to install a rigid product and expecting it to conform to the topography of the substrate. This isnt a realistic expectation and the wood will always be under pressure, trying to rise, working against you and the longevity of the system.

fix the waviness of the concrete floor by grinding the high spots and/or screed patching the lows filling in the voids to get the area to withing acceptable tolerances (say like 1/8" in 6 to 8 feet)

the rest will fall right into place with a flat floor.

as to the anchors, either a powder actuate charge (ramset/hilti) or tapcon type screws you pre-drill the holes for will work.

I prefer the drilling and screwing.

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